The present invention relates generally to a holographic viewing device and a computer-generated hologram for the same, and more particularly to holographic spectacles comprising a hologram mounted on a spectacle frame in such a proper direction as to easily make out the top and bottom and the two sides of the hologram, thereby providing a proper viewing of images in a given form, and a computer-generated hologram for the same.
U.S. Pat. No. 5,546,198 has proposed holographic spectacles constructed as shown in the perspective view of FIG. 8(a). As shown, two transmission type holograms 2 and 3 are fitted in the two-eye sections of a spectacle frame 1. When the spectacles are used to view a scene including such limited extent light sources 4, 5, 6 and 7 as shown in FIG. 8(b), the user would see it as if shown in FIG. 8(c) as an example. In other words, the user would see the pre-selected patterns “NOEL” 8, 9, 10 and 11 in place of the light sources 4, 5, 6 and 7 in the natural scene of FIG. 8(b). For the transmission holograms 2 and 3 having such characteristics, Fourier transform holograms (Fraunhofer holograms) of the aforesaid pattern “NOEL” designed as computer-generated holograms are used.
In a computer-aided Fourier transform hologram, a limited rectangular area including a pattern (“NOEL” as mentioned above) recorded in that hologram is divided into a matrix array of cells, so that information regarding a pattern portion corresponding to each cell site can be allocated to each cell, so that a pattern comprising a limited number of cells is projected onto a hologram area far away from it upon Fourier transform. As is the case with the pattern recording area, the hologram area, too, is divided into a matrix array of cells to record amplitude information and phase information at each cell site where the pattern to be recorded is subjected to Fourier transform.
In the Fourier transform computer-generated hologram with such pre-selected patterns recorded therein, a pattern in a form depending on direction is viewed upon reconstruction. For instance, when the two sides of the hologram are reversed to reverse the left and right sides while the top and bottom remain intact, a mirror image is viewed, in which a right-hand image is seen as a left-hand image. When the top and bottom and the left and right sides of the hologram are reversed while the two sides remain intact, on the other hand, an inverted image is seen, in which an erect image is seen as an inverted image.
Accordingly, unless, upon transmission holograms 2 and 3 comprising such computer-generated holograms mounted on a spectacle frame 1, their top and bottom and their two sides are in proper alignment with the spectacle frame 1, then the viewer could not properly see the pre-selected pattern in a given form.